) plumbonium, (protonated ) Group 15 (pnictogen) onium cations ammonium (IUPAC name azanium), (protonated ammonia (IUPAC name azane)) phosphonium, (protonated phosphine) arsonium, (protonated arsine) stibonium, (protonated stibine) bismuthonium, (protonated bismuthine) Group 16 (chalcogen) onium cations oxonium, (protonated water (IUPAC name oxidane). Oxonium is better known as hydronium, though hydronium implies a solvated or hydrated proton. It may also be called hydroxonium.) sulfonium, (protonated hydrogen sulfide) selenonium, (protonated hydrogen selenide) telluronium, (protonated hydrogen telluride) Group 17 (halogen) onium cations, halonium ions, H2X+ (protonated hydrogen halides) fluoronium, (protonated hydrogen fluoride) chloronium, (protonated hydrogen chloride) bromonium, (protonated hydrogen bromide) iodonium, (protonated hydrogen iodide) Pseudohalogen onium cations aminodiazonium, (protonated hydrogen azide) methylidyneammonium/hydrocyanonium, , isomers HC≡NH+ and N≡CH (protonated hydrogen cyanide) Group 18 (noble gas) onium cations hydrohelium or helonium, better known as helium hydride ion, HeH+ (protonated helium) neonium, NeH+ (protonated neon) argonium, ArH+ (protonated argon) kryptonium, KrH+ (protonated krypton) xenonium, XeH+ (protonated xenon) trifluoroxenonium, ( is neutral.) Hydrogen onium cation hydrogenonium, better known as trihydrogen cation, H (protonated molecular or diatomic hydrogen), found in ionized hydrogen and interstellar space Onium cations with monovalent substitutions primary ammonium cations, RH3N+ or RNH (protonated primary amines) hydroxylammonium, NH3OH+ (protonated hydroxylamine) methylammonium, CH3NH (protonated methylamine) ethylammonium, C2H5NH (protonated ethylamine) hydrazinium, or diazanium, NH2NH (protonated hydrazine, a.k.a. diazane) anilinium (a.k.a. phenylammonium), (protonated aniline, a.k.a. phenylamine, aminobenzene) secondary ammonium cations, R2NH (protonated secondary amines) dimethylammonium (sometimes dimethylaminium), (CH3)2NH (protonated dimethylamine) diethylammonium (sometimes diethylaminium), (C2H5)2NH (protonated diethylamine) ethylmethylammonium, C2H5CH3NH (protonated ethylmethylamine) diethanolammonium (sometimes diethanolaminium), (C2H4OH)2NH (protonated diethanolamine) tertiary ammonium cations, R3NH+ (protonated tertiary amines) trimethylammonium (CH3)3NH+ (protonated trimethylamine) triethylammonium (C2H5)3NH+ (protonated triethylamine) quaternary ammonium cations, R4N+ or NR tetrafluoroammonium, NF tetramethylammonium, (CH3)4N+ tetraethylammonium, (C2H5)4N+ tetrapropylammonium, (C3H7)4N+ tetrabutylammonium, (C4H9)4N+ or abbreviated Bu4N+ trimethyl ammonium compounds, (CH3)3RN+ didecyldimethylammonium, (C10H21)2(CH3)2N+ pentamethylhydrazinium, N(CH3)2N(CH3) quaternary phosphonium cations, R4P+ or PR tetraphenylphosphonium, primary oxonium cations, (protonated R-O-H oxygen compounds) alkyloxonium cations (protonated alcohols) methyloxonium, (protonated methanol) ethyloxonium, (protonated ethanol) secondary oxonium cations, (protonated R-O-R oxygen compounds) dialkyloxonium cations (protonated ethers) dimethyloxonium, (protonated dimethyl ether) tertiary oxonium cations, trifluorooxonium, (hypothetical) trimethyloxonium, triethyloxonium, oxatriquinacene, (cyclic) oxatriquinane, (cyclic) secondary sulfonium cations, R2SH+ (protonated sulfides) dimethylsulfonium, (CH3)2SH+ (protonated dimethyl sulfide) tertiary sulfonium cations, R3S+ trimethylsulfonium, (CH3)3S+ secondary fluoronium cations, R2F+ dichlorofluoronium, Cl2F+ Onium cations with polyvalent substitutions secondary ammonium cations having one double-bonded substitution, diazenium, (protonated diazene) guanidinium, (protonated guanidine) (has a resonance structure) tertiary ammonium cations having one triple-bonded substitution, R≡NH+ nitrilium, RC≡NH+ (protonated nitrile) diazonium, N≡NH+ (protonated nitrogen)